page_title: Marstonia comalensis
section_title: Shell description
hierarchical_section_title: Marstonia comalensis / Shell description
caption_attribution_description: English: Photo of the inner side of the operculum of Marstonia comalensis USNM 874926. Scale bar is 200 μm.
context_page_description: Marstonia comalensis is a species of minute freshwater snail with a gill and an operculum, an aquatic gastropod mollusk or micromollusk in the family Hydrobiidae. It is found in south central Texas, United States.
  Marstonia comalensis is large for this genus. It has an ovate-conic, openly umbilicate shell. The penis has a short filament and oblique, squarish lobe bearing a narrow gland along its distal edge. It is well differentiated morphologically from other congeners that have similar shells and penes, and is also genetically divergent relative to those congeners that have been sequenced.
  This species has often been confused with Cincinnatia integra.
context_section_description: The shell is ovate-conic with 4.5–5.5 whorls. The height of the shell is about 2.6–4.6 mm. Protoconch is near planispiral, slightly tilted, initial 0.75–1.0 whorl strongly wrinkled. Teleoconch whorls are weakly convex, often narrowly shouldered, rarely having subsutural angulation. The sculpture of strong collabral growth lines, later whorls having numerous weak spiral striae. The aperture is pyriform or ovate. Inner lip complete across parietal wall in larger specimens, usually narrowly adnate, rarely slightly disjunct; usually thin, sometimes slightly thickened apically; columellar shelf absent or very narrow; outer lip thin or slightly thickened, orthocline or prosocline. Umbilicus is open but small.
  The operculum is thin, amber, narrowly ovate, multispiral with eccentric nucleus. The last 0.25 whorl is sometimes frilled on outer side; inner side having well developed rim near outer edge. The attachment scar border is sometimes weakly thickened near the nucleus.
caption: Photo of the inner side of the operculum. Scale bar: 200 μm.
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